Orbiting Spacecraft Galileo

The Galileo mission to Jupiter was the first space mission designed to place a spacecraft into orbit about a giant planet and also the first space mission to deploy an entry probe directly into the atmosphere of such a planet. The Galileo spacecraft, managed by JPL, was a huge structure with a mass of 2,223 kg and was over 6 m tall (Figure 7.37). The spacecraft used a novel "dual-spin" design with a top section, incorporating the communications systems, booms, and other systems, spinning at 3 rpm and a lower three axis-stabilized section, upon which the remote-sensing instruments were placed on a pointable platform allowing them to stop and look in almost any direction. The Galileo entry probe was stowed at the bottom of the spacecraft until it was deployed on approach to Jupiter. The spacecraft was named after Galileo Galilei (1564-1642), who first observed Jupiter's major moons: Io, Europa, Ganymede, and Callisto, now known as the Galilean satellites, in January 1610.

The spacecraft was launched on October 18, 1989 from Cape Canaveral onboard the space shuttle Atlantis and embarked upon an extended Venus-Earth-Earth Gravity Assist (VEEGA) trajectory to Jupiter, as shown in Figure 7.38, before going into orbit about that planet on December 7, 1995. Six months prior to its arrival, the probe was deployed, which then proceeded purely under its own momentum and the pull of Jupiter's gravity, before entering the atmosphere just prior to the entry of the main part of the spacecraft into Jupiter orbit.

The orbital design of Galileo's tour primary is shown in Figure 7.39 and the distance at each perijove was typically 15 Rj. The high eccentricity of the orbits allowed Galileo to not only pass close to Jupiter on each revolution, but also to pass

Figure 7.38. Galileo interplanetary trajectory. Courtesy of NASA.

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